The disposal of waste vegetation, such as trees, brush, yard waste, etc. is a major concern of the municipal, commercial, and private sectors. Various types of recycling equipment and techniques are in use or have been proposed to dispose of such waste, all with varying degrees of success.
One method of disposal is to transport and bury the waste in a landfill. However, landfill sites are becoming scarce and those remaining are cost prohibitive especially in rapidly growing urban areas. In addition, even if suitable sites can be found, they are often at a distance that makes transportation cost prohibitive. Since vegetation waste makes up approximately 40% of the bulk typically buried in landfills, most large cities require that the waste be separated from conventional garbage for purposes of mulch and compost manufacture in an effort to recycle the waste.
Each year there are tens of thousands of acres of land cleared of trees, brush, etc. for development and millions of tons of yard waste (small branches, leaves, grass, etc.) produced. Reducing the amount of such waste being buried or mulched would significantly reduce the pressure on existing landfills and delay the need for opening new landfill sites. In addition, landfills are a relatively inefficient method of recycling. Being simply buried at one site, the economic potential of the waste material is never fulfilled. Therefore, there is a need for an alternative disposal process capable of diverting such waste material from already over-crowded landfills to allow the commercial sector to process and sell products produced from the waste material.
One option to landfills has been to incinerate the waste material. This produces an ash residue which is extremely high in natural nutrients beneficial for plant growth. When the ash is mixed with compost and varying amounts of soil, a range of products from high-grade potting soil to top soil are developed. Open burning of the vegetation waste on site is the simplest and most cost effective way of incinerating the waste material. However, due to the many environmental limitations imposed by Federal, State, and local jurisdictions, open burning is not always feasible or possible. Many such regulations significantly limit the amount of ash and smoke that may be released into the atmosphere.
Air curtain incinerators such as that disclosed in U.S. Pat. No. 4,756,258 were developed to permit the incineration of such vegetation waste while minimizing the amount of ash and smoke being released. With such an incinerator, the vegetation waste is loaded into a fire pit through an opening and ignited. High velocity air from a manifold positioned along the opening is then blown over and into the pit. The manifold disclosed in the '258 patent distributed the high velocity air such that a greater amount of air exited the manifold at its center and outer-most ends compared to its intermediate sections (i.e., between the center and the two ends). This non-uniform air flow pattern was intended to cause a down-draft to form pulling outside air into the pit rather than releasing smoke and ash into the atmosphere. However, this blower system has proved to be inadequate in preventing the controlled release of smoke and ash. In addition, because the vegetation waste must be transported to the fire pit, this particular incineration technique has the added drawback of the associated transportation costs.
Another drawback of open pit incineration is the need for creation of the pit. This requires the employment of an earth mover and an operator familiar with pit construction. In many instances neither an earth mover or a qualified operator is available and timber is incinerated in an open stance. This poses additional problems in that wind gusts could cause the loss of fire control.